The following FIRCA application describes a proposed collaborative effort between the laboratories of Dr. Michael J. Behe, Department of Chemistry, Lehigh University, and Dr. Jaroslav Kypr, Institute of Biophysics, Czechoslovak Academy of Sciences. In the collaborative effort the laboratory of Dr. Behe will synthesize and send to Dr. Kypr's laboratory a range of synthetic polydeoxynucleotides which Dr. Behe's laboratory is currently making in connection with work funded under the parent grant. The laboratory of Dr. Kypr will then examine the polynucleotides for transitions to the A, X, and triplex DNA conformations as a function of the repeating unit of the polynucleotide. The experiments will take advantage of the extensive experience of Dr. Kypr's lab with studies of DNA conformational isomerizations using circular dichroism (CD) spectroscopy and other methods. In parallel with CD, Dr. Kypr's laboratory will irradiate the polynucleotides with uv light and analyze the irradiated polynucleotides by denaturing gel electrophoresis. Such experiments are motivated by preliminary results showing that the interstrand crosslinking, when irradiated in the X-DNA conformation, but not when irradiated in the B-DNA or A-DNA conformations.